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MARINE IN SITU BURNING OF OIL: QUESTIONS AND ANSWERS FOR COMMUNICATING WITH THE PUBLIC GENERAL Q. What is in situ burning? In situ burning is the combustion of an oil spill on the water (in situ is Latin for in place). In situ burning (or ISB) involves controlled burning of spilled oil. Typically, the oil is contained within a fire-resistant boom and ignited using an igniter from a helicopter. The burn continues only as long as the oil is thick enough, usually about 1/10 of an inch or 2-3 millimeters, so containment is important to sustain the burn. When conducted properly, in situ burning significantly decreases the amount of oil on the water, reducing the extent of shoreline impacts, including exposure of sensitive natural, recreational, and commercial resources. ISB is viewed with growing interest as a response tool. Burning can rapidly remove a large volume of oil from the surface of the water, reducing the magnitude of subsequent environmental impacts. In areas such as high-latitude waters where other techniques may not be possible or advisable due to the physical environment (e.g. ice flows and extreme low temperatures) or the remoteness of the region, burning may represent one of the few viable response choices besides no action. In addition, the magnitude of a spill may overwhelm the containment and storage equipment deployed or available for a region, necessitating the consideration of other response methods. ISB may offer a logistically simple, rapid, inexpensive, and relatively safe means for reducing the shoreline impacts of an oil spill. Moreover, because a large portion of the oil is converted to gaseous combustion products, the need for collection, storage, transport, and disposal of recovered material can be subsequently reduced. For these and other reasons, ISB is gaining attention and favor as an oil spill response technique. While this document is focused on marine/off shore ISB, in situ burning can be a valuable response option for oil spilled in inland and upland habitats. In situ burning may be appropriate in inland and upland habitats when 1) oil needs to be removed quickly to prevent the spread of contamination or further environmental damage 2) spill locations are remote or have restricted access due to terrain or other factors and 3) other cleanup options prove ineffective or threaten to be more harmful to the environment. Q. Is in-situ burning an effective way to remove oil from the water? Although the efficiency ofISB is highly dependent on a number of physical factors, test burns and applications in actual spill situations suggest that ISB can be very effective in removing large quantities of oil from the water. Under the right environmental and oil conditions, burning can remove up to 95-98% of the oil contained in the fire-resistant boom. While all spilled oil cannot generally be burned, especially in large spills, ISB can remove large quantities of oil from the water, significantly reducing the extent of shoreline impacts. ISB is more effective in removing crude oil than other types of oil from the water surface; with lighter, lower viscosity oils it is difficult to maintain the necessary slick thickness and heavier, less volatile oils are difficult to ignite. Q. What are the controlling and limiting factors for in-situ burning? Although ISB is a relatively simple technique, spill circumstances can limit its safe and efficient application. Whether and how oil burns is the result of a number of physical factors related to the oil itself and the extent to which the oil has been exposed to the environment. Critical factors such as oil thickness, degree of weathering, and extent of emulsification generally change with the passage of time, and the changes that occur make it more difficult to burn the oil. As a consequence, ISB is most easily and effectively implemented during the early stages of a spill (generally the first 12 hours for marine ISB; on land time is less critical). The basic criteria applied when considering using ISB are the following: 1. That human populations will not be exposed to smoke that exceeds state and federal health standards